Use Zend2 (#39)

Author: Nyholm

composer.json

@@ -20,10 +20,10 @@
     },
     "require-dev": {
         "guzzlehttp/psr7": "^1.4",
-        "nyholm/psr7": "dev-master",
+        "nyholm/psr7": "^1.0",
         "ringcentral/psr7": "^1.2",
         "slim/psr7": "dev-master",
-        "zendframework/zend-diactoros": "^1.8"
+        "zendframework/zend-diactoros": "^2.1"
     },
     "extra": {
         "branch-alias": {